Modular buildings are those built using prefabricated volumetric units called modules. Due to modules being connected to each other at discrete locations, discontinuous structural systems are formed, where diaphragm discontinuity is a key issue and could result in diaphragms that are flexible. Multi-story modular buildings with flexible diaphragms are susceptible to higher mode influences when under the action of seismic loads, where such influences affect lateral load distribution, cause excessive drift among gravity frames and could potentially lead towards collapse.
This paper presents the preliminary work conducted to classify the behaviour of diaphragms in modular buildings and to assess the effects of diaphragm flexibility on the overall seismic performance of a case study modular building. Diaphragm behaviour was controlled through axial and shear stiffness of diaphragm connections as well as the combined shear stiffness of adjacent module floor and ceiling units. Seismic analyses were conducted using 44 scaled far-field ground motions as considered within FEMA P695 and the results indicate that the case study modular building with flexible diaphragms is affected by higher modes and current code provisions are inadequate for the seismic design of modular buildings.